Laterally cyano- and fluoro-substituted terphenyls

ABSTRACT

Laterally cyano-substituted terphenyls of formula (I), wherein R 1  and R 2  are independently selected from hydrogen or C 1-15  alkyl, alkoxy, or alkyl or alkoxy in which one or more CH 2  groups are replaced by O, COO, OOC, CHX, CX 2 , CH=CX, CX=CH, CX=CX, where X is fluorine or chlorine. CRCN where R is alkyl, or C.tbd.C or in which a terminal CH 3  of the said alkyl or alkoxy chain is replaced by CF 3 , n is 0 or 1, and the CN and F (if present) substituent are independently located in any of the available substitution positions. Liquid crystal materials containing these terphenyls are also described.

This is a continuation application Ser. No. 07/469,486, filed Apr. 11,1990, now abandoned.

This invention relates to laterally cyano- substituted terphenyls, inparticular to those which may be used as constituents of liquid crystalmixtures. The invention also relates to such mixtures containing theseterphenyls and to electro-optic devices which use them.

BACKGROUND OF THE INVENTION

Liquid crystal materials are well known, and are commonly used inelectro-optical devices such as watches, calculators, displays etc. Suchmaterials are of two general types. There are those which use theelectro-optical properties of the nematic (N) phase, such as theelectrically controlled birefringence (ECB) effect, as described in M.F. Schieckel and K. Fahrenshon, "Defomation of nematic liquid crystalswith vertical orientation in electrical fields". Appl Phys Left (1971),19, 3912. There are also those which use the electrooptical propertiesmanifested by smectic phases. Examples of the latter include theferroelectric effect manifested by certain chiral tilted smectic phases,see for example N A Clark and S T Lagerwall Appl-Phys Left (1980) 36,899 which offers the advantages of high speed and bistable properties.The chiral smectic C, F and I phases (S_(C) * S_(F) * and S_(I) I (theasterisk denoting chirality) are generally most favoured for such userthe S_(C) * being preferred because of its lower viscosity. Anotherelectro-optical effect in smectic phases is the fast-switchingelectroclinic effect manifested by smectic A phases (S_(A)).

Nematic and ferroelectric smectic liquid crystal materials have a numberof desirable requirements in common, which for example include ease ofpreparation, chemical and photochemical stability, low viscosity and abroad temperature range over which the useful phases (eg N, S_(C), S_(F)or S_(I)) persist. Such materials are generally mixtures of compoundsand these requirements are sought in compounds or mixtures thereofintended for use in the materials.

Materials and compounds for use in ECB devices and S_(C) * devices havea number of specific desirable requirements. For example for use in ECBdevices, compounds and materials should preferably show a high value forthe ratio of elastic constants K₃ /K₁, high values for the opticalanisotropy Δn and a negative dielectric anisotropy ΔE. Indevices whichuse the ferroelectric effect in S_(C) * materials it is desirable thatcompounds and mixtures show an S_(A) phase at a temperature above therange over which the S_(C) * phase persists, and that undesirable phasessuch as S_(B) do not appear.

A number of compounds are known which show broad S_(C) phases, amongwhich are the alkyl- or alkoxy- terminated fluoroterphenyls ("FTP's")described in EP-A-0132377, of general formula: ##STR1## where R₁ and R₂are alkyl or alkoxy. Some FTPs and mixtures thereof are known to showbroad temperature range S_(C) phases. This has made them excellentcandidates for constituents of ferroelectric smectic mixtures. See forexample their use in the mixtures disclosed in PCT/GB 87/0441 and GB8627107.

It is an object of the present invention to provide novel compoundswhich may be used as constituents of liquid crystal mixtures, and novelliquid crystal mixtures which incorporate them.

According to this invention novel laterally cyano-substituted terphenylsof general formula I below are provided: ##STR2## wherein R¹ and R² areindependently selected from hydrogen or C₁₋₁₅ alkyl, alkoxy, or alkyl oralkoxy in which one or more CH₂ groups are replaced by O, COO, OOC, CHX,CX₂, CH=CX, CX=CX, where X ia Fluorine or chlorine, CRCN where R isalkyl, or C.tbd.C, or in which X is terminal. CH₃ of the said alkyl oralkoxy chain is replaced by CF₃, n is 0 or 1, and the CN and F (ifpresent) substituent are independent located in any of the availablesubstitution positions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-11 illustrate various synthetic routes for preparing thecompounds of Formula I retaining the structures of Table 1 to synthesisroutes A-F; and

FIG. 12 is a cross-sectional view of a liquid crystal electro opticaldisplay device containing a liquid crystal material of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The structural preferences discussed below are based on inter alia onease of preparation and suitability for use as constituents of liquidcrystal mixtures and electro-optical devices which use them.

Preferred structures for terphenyls of formula I are those having ageneral formula IA below: ##STR3## wherein R¹ and R² independentlyalkyl, alkoxy or alkynyl, and the terphenyl has a substitution patternselected from any one of the following substitution patterns: (D=CN),(A=CN), (B=F, G=CN), (A=CN, B=F), (n=CN), (C=CN, D=F), (A=F, G=CN),(A=F, E=CN), (B=F, E=CN), (B=F, D=CN), (A=F, D=CN), (A=F, C=CN), (B=F,C=CN), (A=F, B=CN) the remaining lateral substitution positions beingoccupied by hydrogen.

The structures included in formula IA are listed below in Table 1.

                  TABLE 1                                                         ______________________________________                                         ##STR4##                   1.1                                                ##STR5##                   1.2                                                ##STR6##                   1.3                                                ##STR7##                   1.4                                                ##STR8##                   1.5                                                ##STR9##                   1.6                                                ##STR10##                  1.7                                                ##STR11##                  1.8                                                ##STR12##                  1.9                                                ##STR13##                  1.10                                               ##STR14##                  1.11                                               ##STR15##                  1.12                                               ##STR16##                  1.13                                               ##STR17##                  1.14                                              ______________________________________                                    

R¹, R² =alkyl, alkoxy or alkynyl of the structures listed in Table 1,structures 1.1, 1.3, 1.4, 1.5, 1.6 and 1.10 are particularly preferred,especially 1.1, 1.3, 1.4, 1.10.

In compounds of formula I, IA or as listed in Table 1, R¹ and R² arepreferably independently n-alkyl, n-alkoxy or n-alkynyl containing 3-12especially 3-10 carbon atoms, or branched or asymmetrically substitutedalkyl, alkoxy or alkynyl, which may be in an optically active or racemicform, but especially n-alkyl or n-alkoxy. R¹ and R² may be the same ordifferent.

In a compound of formula 1, R¹ and R² may therefore be independentlydently selected from the following preferred groups listed in Table 2below:

                  TABLE 2                                                         ______________________________________                                        n-alkyl       n-alkoxy     n-alkynyl                                          ______________________________________                                        C.sub.3 H.sub.7                                                                             C.sub.3 H.sub.7 O                                                                          C.sub.2 H.sub.5 C.tbd.C                            C.sub.4 H.sub.9                                                                             C.sub.4 H.sub.9 O                                                                          C.sub.3 H.sub.7 C.tbd.C                            C.sub.5 H.sub.11                                                                            C.sub.5 H.sub.11 O                                                                         C.sub.4 H.sub.9 C.tbd.C                            C.sub.6 H.sub.13                                                                            C.sub.6 H.sub.13 O                                                                         C.sub.5 H.sub.11 C.tbd.C                           C.sub.7 H.sub.15                                                                            C.sub.7 H.sub.15 O                                                                         C.sub.6 H.sub.13 C.tbd.C                           C.sub.8 H.sub.17                                                                            C.sub.8 H.sub.17 O                                                                         C.sub.7 H.sub.15 C.tbd.C                           C.sub.9 H.sub.19                                                                            C.sub.9 H.sub.19 O                                                                         C.sub.8 H.sub.17 C.tbd.C                           C.sub.10 H.sub.21                                                                           C.sub.10 H.sub.21                                                                          C.sub.9 H.sub.19 C.tbd.C                           C.sub.11 H.sub.23                                                                           C.sub.11 H.sub.12 O                                                                        C.sub.10 H.sub.21 C.tbd.C                          C.sub.12 H.sub.25                                                                           C.sub.12 H.sub.25 O                                             ______________________________________                                    

Preferred asymmetrically substituted alkyl and alkoxy groups are2-methylbutyl, 2-methylbutyloxy, 3-methylpentyl, 3-methylpentyloxy,4-methylhexyl, 4-methylpentyl, 1-methylheptyl and 1-methylheptyloxy.

Preferred asymmetrically substituted alkynyl groups are: ##STR18##

Compounds of formula I may be prepared via a number of synthetic routes,for example routes A - F shown in the accompanying FIGS. 1-11, route Bproviding some useful intermediates. The respective structural typeswhich may be prepared using these routes are as follows, referring toTable 1 above:

    ______________________________________                                        Structure             Route                                                   ______________________________________                                        1.1                   A1, A2                                                  1.2                   C1                                                      1.3                   C1, C2                                                  1.4                   D1, D2                                                  1.5                   D3                                                      1.6                   D4                                                      1.7                   E1, E2                                                  1.8                   E1                                                      1.9                   E1                                                      1.10                  E1, E2                                                  1.11                  F1                                                      1.12                  F2                                                      1.13                  F3                                                      1.14                  F4                                                      ______________________________________                                    

Modifications to routes A-F to prepare compounds in which thesubstituents R₁ and R₂ of Table 1 are different to those illustrated inFIGS. 1 to 11 will be apparent to those skilled in the art of organicsynthesis, for example the replacement of the alkyl or alkoxy groups R,R¹, R² R" by their perfluorinated analogues or by alkynyl or alkynyloxygroups.

Although the overall routes A-F and their end products are novel theindividual steps use known reactions.

For example the following steps use the known coupling reaction betweenthe halo-phenyl ring and the phenylboronic acid in the presence oftetra-(triphenylphosphine)-palladium (0): A11, A23, A24, C14, C23, C25,D13, D22, D42, D44, El2, E22, E23, F11, F21, F31, F32, F43, F

The phenylboronic acids used in these steps may in turn be produced fromthe halophenyl precursor by the known method which first prepares aGrignard Reagent using Magnesium in tetrahydrofuron (THF) followed by areaction with tri-isopropylborate then hydrolysis with hydrochloricacid. This procedure is used in steps B13, B22, C13, D41, D43, E11, F42.

In routes D1, D2, D3 and D4 the lateral CO₂ H group is introduced intothe fluorinated ring using n-Butyl-lithium in hexane followed byreaction with carbon dioxide then hydrolysis. The CO₂ H group is thenconverted into the corresponding amide using oxalyl chloride andammonia, followed by dehydration using thionyl chloride.

Other known reactions used in these routes are as follows:

A21, F45 - N-bromosuccinimide/dichloromethane 0° C.

A22, F46 - (i) NaNO₂ HCl (ii) KI

B11 - Friedel Crafts reaction, RCOCl/AlCl₃

B12, F48 - via hydrazine hydrate (F48a=direct use)

B21, C11, D21, F41 - RBr/acetone/K₂ CO₃

C12 - Br₂

C21, P47- R-C.tbd.CH, ZnCl₂ : Pd(PPh₃)₄

C22- H2, Pd/C

Apart from standard reagents the starting materials for routes A-F areknown or commercially available, eg from BDH Ltd or Fluorochem. A methodfor the preparation of the terphenyl starting point of route D3 is foundin EP-A-0132377. In routes A-F when the starting compound may be made byone or more of the other routes this is indicated, eg (C13) in route C2shows that this starting compound may be made via step C13.

It should also be noted that the products of steps D13, D22 and D43, andthe starting compound for step D31 are protected by the claims of theApplicant's EP-0132377-B and U.S. Pat. No. 4,594,465.

To prepare compounds in which R¹ and/or R² contain fluorine, theappropriate perfluoroalkyl compounds may be used as starting points, egin steps B11 or B22 etc.

Compounds in which R¹ and/or R² contain a COO or OOC group, e.g. RCOO-where R is alkyl may for example be prepared by removing a terminal R¹or R² group which is alkoxy from a terphenyl product of formula I or IAusing the known method of reaction with BBr₃ followed by hydrolysis toleave a terminal -OH group, followed by esterification of phenol with acarboxylic acid RCOOH or an acyl chloride RCOCl.

The C.tbd.C group in compounds in which R¹ and /or R² is alkynyl is areactive functional group and may for example be hydrated, eg usingHgSO₄ /H₂ SO₄ or B₃ to yield terminally ketone substituted terphenyls,eg having terminal --CO.CH₂, --R or --CH₂ CO.--R groups. Such ketonesmay be reduced to form the corresponding alcohols, i.e. --CH(OH)CH₂ --Ror --CH₂ CH(OH)--R which themselves be esterified with a carboxylic acidto form the corresponding esters.

Alterately the ketones may be converted into cyanohydrins by reactionwith HCN, leaving terminal groups of structure --C·N·OH--CH₂ --R and--CH₂ --C·CN·R. Such cyanohydrins may then be esterified eg with acarboxylic acid R"--COOH where R" is alkyl to yield terphenyls with oneor more terminal substituent groups of structure: ##STR19##

Also reaction of the C.tbd.C group with halogens or hydrogen halides canlead to terphenyls of formula. I with halogenated terminal substituentsR¹ and/or R². For example well known reactions of an alkyne substituentR-C.tbd.C such as in the product of step C25 can lead in this way toR--CX₂ CX₂ --, R--CHX=CHX--, R--CH₂ CX₂ --) and R--CX₂ CH₂ -- where X isa halogen eg chlorine.

Many terphenyls of formula I show liquid crystal phases, and also a highnegative dielectric anisotropy ΔE. These are therefore useful componentsof liquid crystal materials, and therefore according to a further aspectof this invention there is provided a liquid crystal material, being amixture of compounds, at least one being a terphenyl of formula I,preferably formula IA.

Such a liquid crystal material may be a nematic or smectic liquidcrystal material.

A nematic liquid crystal material may therefore be a mixture ofcompounds at least one of which is a terphenyl of formula I, preferablyone which exhibits a nematic liquid crystal phase. As terphenyls offormula I have a high negative ΔE they may usefully be mixed with othercompounds which show nematic liquid crystal phases and which for examplehave a low ΔE, or a positive ΔE to provide a mixture of intermediate ΔE.As is well known in the liquid crystal art, the sign of ΔE (ie +ve or-ve) of a nematic liquid crystal material is chosen according to thekind of electro-optical device in which the material is to be used.Hence the availability of the high negative ΔE compounds of theinvention is very advantageous. In particular the terphenyls of theinvention are likely to be useful in liquid crystal mixtures which usethe ECB effect.

The general classes of other compounds which may be included in anematic liquid crystal material according to this aspect of theinvention will be well known to those skilled in the liquid crystal art.Some examples of compounds having a low ΔE are listed below: ##STR20##

Some examples of compounds having a positive ΔE are listed below:##STR21##

Where R and R' independently represent C₁ -C₈ alkyl or alkoxy, and Xrepresents F or H.

The nematic liquid crystal mixture of this aspect of the invention myalso contain pleochrotc dyes, such as those described in EP-A-82300891,and/or One or more optically active compounds to induce the appearanceof a cholesteric phase.

Typically but not exclusively a nematic liquid crystal mixture of thisaspect of the invention contains:

Compounds of formula I: 5-95 wt %

Low ΔE compounds: 0-95 wt %

High +ve ΔE compounds: 9-95 wt %

Optically active compounds: 0-5 wt %

Pleochroic dyes: 0-5 wt %

The over-all sum of weight percentages being 100 wt %.

The invention also provides a smectic liquid crystal material which is amixture of two or more compounds, at least one of which is a terphenylof formula I, preferably of formula 1A, and especially of formula 1.1 or1.4 of Table 1. This mixture preferably also contains in addition one ormore other compounds which together-or separately show a smectic phase.The smectic phase is preferably S_(C), S_(F) or S_(I) /

Preferably the mixture of this aspect of the invention contains one ormore terphenyls of formula I and one or more FTP's of formula II##STR22## where R³ and R⁴ are independently selected from hydrogen,alkyl and alkoxy each containing 1-12 carbon atoms, p may be 1 or 2 andthe fluorosubstituents(s) may occupy any of the available lateralsubstitution positions. Preferred FTP's for this aspect of the inventionhave a formula IIA, IIB or IIC. ##STR23## where R³ and R⁴ are as definedabove, and where X and Y are independently selected from hydrogen andfluorine, at least one of X and Y being fluorine. Preferably R³ and R⁴are n-alkyl or n-alkoxy containing 3-12 carbon atoms, especially 3-10.

R³ and R⁴ may be the same or different. Preferred n-alkyl and n-alkoxygroups from which R³ and R⁴ may be selected are those from which R¹ andR² are selected, as listed above, although the combinations of R¹ and R²need not be the same as R³ and R⁴ in the mixture.

Preferably X in formula IIA is hydrogen and Y is fluorine. Thepreparation of such FTPs is described for example in EP-A-0132377. Thepreparation of FTPs in which p is 2, eg of formula IIB and IIC isdescribed in GB-A-8806220 filed 16-03-88, the contents of which areincorporated herein by reference.

The smectic liquid crystal material of this aspect of the invention mayfor example show an Sc phase at room temperature, and may be a mixtureof one or more FTPs of formula IIA plus one or more terphenyls of theinvention, or may be a mixture of one or more FTP's of formula IIB andor one or more FTP's of formula IIC plus one or more terphenyls of theinvention.

The addition of one or more compounds of formula I to one or more FTPsof formula II often results in suppression of undesirable S_(B) phasesshown by the FTP, and may also result in a mixture showing an S_(C)phase over a broader temperature range than the FTP. This isparticularly so with FTP's of formula IIA. These effects may bemanifested at quite low ratios of formula I compound(s) to FTP's, forexample typically in the range 1:20 to 1:5 by weight % of formula Icompound(s) to FTP(s).

Other compounds which show an S_(C) phase and which may be used inmixtures of this aspect of the invention are the known compounds:##STR24## where R^(A), R^(B) and R^(C) independently contain 1-12 carbonatoms, R^(A), and A^(B) are independently n-alkyl or n-alkoxy, and R^(C)is independently n-alkyl.

With the smectic mixtures of this aspect of the invention may be mixedone or more optically active compounds which induce the mixture to showan S_(C) * phase and/or increase the P_(S) of the mixture. The mixturesproduced in this way are ferroelectric mixtures showing a P_(S) valueand are a further aspect of this invention. The use of terphenyls of theinvention in such mixtures may result in advantageous P_(S) values andswitching times.

Many optically active compounds are known which may be used in this way.Preferred optically active compounds are those described in PCT GB85/0512, eg ##STR25## the compounds described in EP-A-0110299, eg##STR26## the compounds described in PCT/GB 87/00280, eg ##STR27## andin particular the compounds described in PCT/GB87/00441 which contain aCOOCH(CN)R group where R is alkyl, for example: ##STR28## where R^(A) isn-alkyl or n-alkoxy containing 5-12 carbon atoms, (F) indicates that thephenyl ring may carry a fluoro substituent, and R^(B) is C₁ -4 n-alkyl,cycloalkyl or a branched alkyl of formula: ##STR29## where a may be 0 oran integer 1-5, and each of b and c is an integer 1-6, preferably abeing 0 and at least one of b or c being 1.

Preferred groups R^(B) in compounds VII are methyl, --CH(CH₃)₂, --CH·C₃·CH₂ CH₃ and cyclohexyl.

Additives if used in such mixtures may fulfill a number of functions.For example additional optically active compounds may be included tocontrol the pitch of the S_(C) *, phase such as the optically activeamide compounds described in PCT GB 87/00223, eg ##STR30## or theoptically active terphenyls described in GB 8703103 eg ##STR31## whereR^(A), R^(B) and R^(C), are independently n-alkyl or n-alkoxy containing1-12 carbon atoms, D is F or C;, X is OOCCH(CH₃)OR", OCH(CH₃)COOR" orCOOCH(CH₃)R" where R" is n-alkyl containing from 1 to 12 carbon atoms.

Additives may also serve the function of encouraging the formation of anS_(A) phase at a temperature above that of the S_(C) * to assist inalignment of the mixture with the electrodes of an electro-optic device.

Additives may also suppress undesirable phases such as S_(A) or S_(B) sothat these occur at temperatures far away from the working temperaturerange, eg ##STR32## where R^(A) and R^(B) are independently n-alkyl orn-alkoxy containing 1-12 carbon atoms.

Typically but not exclusively a smectic C liquid crystal material ofthis aspect of the invention is a mixture having a composition asfollows:

    ______________________________________                                        One or more compounds which show                                                                   50-95       wt %                                         together or separately a room                                                 temperature S.sub.C phase,                                                    especially of formulae IIA, IIB                                               IIC or IIIA.                                                                  Compound(s) of formula I.                                                                          5-50        wt %                                                              preferably 5-25                                                                           wt %                                         Optically active compound(s), at least                                                             0-25        wt %                                         some being present if the mixture is to                                       show an S.sub.C phase.                                                        Additive(s)          0-20        wt %                                         Total                100         wt %                                         ______________________________________                                    

The nematic and ferroelectric smectic liquid crystal mixtures of theinvention may be used in any of the known types of liquid crystalelectro-optical display device which use such materials, for example asdescribed in the two Appl. Phys. Left. references mentioned above.

The construction and method of operation of such liquid crystalelectro-optical devices is well known. Generally such a device comprisestwo substantially parallel substrates, at least one of which isoptically transparent, and having electrodes on their facing surfaces,and sandwiched between them a liquid crystal material. The applicationof a voltage across the liquid crystal material via the electrodescauses a change in the optical properties of the liquid crystal materialto produce a visible effect. Suitable dimensions, voltages and otherparameters for such a device will be apparent to those skilled in theart.

The invention will now be described by way of example only withreference to the accompanying FIGS. 1-11 whch show preparative routesfor terphenyls of the invention and FIG. 12 which shows a cross sectionthrough a liquid crystal device.

In the following examples all temperatures are in °C. The abbreviationN=nematic, S_(A) =smectic A, S_(C) =smectic C, S_(?) and S_(??])unidentified smectic phase I=isotropic liquid K=solid crystal. Liquidcrystal transitions shogun () are virtual transitions seen onsupercooling.

PREPARATION EXAMPLES EXAMPLE 1

Using routes A1, A2, B1 and B2 the following compounds of structure 1.1were made:

    ______________________________________                                         ##STR33##                                                                    R.sup.1  R.sup.2   Liquid crystal transition temps (°C.)               ______________________________________                                        n-C.sub.5 H.sub.11                                                                     n-OC.sub.6 H.sub.13                                                                     K 35.5 S.sub.A 97.5 I                                      n-C.sub.5 H.sub.11                                                                     n-OC.sub.8 H.sub.17                                                                     K 33.5 S.sub.A 103.0 I                                     n-C.sub.6 H.sub.13 O                                                                   n-C.sub.5 H.sub.11                                                                      K 48.5 (S.sub.C 29.5) N 77.5 I                             n-C.sub.8 H.sub.17 O                                                                   n-C.sub.5 H.sub.11                                                                      K 35 0 S.sub.C 42.0 N 78.0 I                               n-C.sub.6 H.sub.13 O                                                                   n-OC.sub.6 H.sub.13                                                                     K 101.5 (S.sub.C 61.0) S.sub.A 110.0 N 114.0 I             n-C.sub.5 H.sub.11                                                                     n-C.sub.5 H.sub.11                                                                      S.sub.A -N (33.5) N-I (38.0) K-I 40.0                      n-C.sub.6 H.sub.13                                                                     n-OC.sub.6 H.sub.13                                                  ______________________________________                                    

Route B1

Step B11

The compound ##STR34## was prepared by a Friedel - Crafts reactionbetween bromobenzene and n-pentanoyl chloride (C₄ H₉ COCI) in thepresence of aluminium chloride.

Step B12 ##STR35##

A mixture of the product of step B11 (77.1 g, 0.32 mol), hydrazinchydrate (46.4 g, 0.93 mol) and potassium hydroxide (59.0 g, 1.05 mol) indiethylene glycol (250 ml) was heated at 130° C. for 2 h. The excess ofhydrazine hydrate was distilled off and the temperature was raised to 0°C. for 2 h. The cooled mixture was poured into 18% hydrochloric acid,the product was extracted into ether (twice), and the combined etherealextracts were washed with water and dried (MgSO₄). The solvent wasremoved in vacuo and the residue was distilled to yield a colourlessliquid. The identity of the product was confirmed by nmr, ir and MS.Yield 58,1 g (80%), bp 145°-148° C. at 20 mm Hg.

Step B13 ##STR36##

A solution of the Grignard reagent prepared from the product of step B12(24.0 g, 0.11 mol) and magnesium (2.95 g, 0.12 mol) in dry THF (85 ml)was added dropwise to a stirred, cooled (-78° C.) solution oftri-isopropyl borate (39.8 g, 0.21 mol) in dry THF (25 ml) under drynitrogen. The stirred mixture was allowed to warm to room temperatureovernight and stirred for 1h with 10% hydrochloric acid (120 ml) at roomtemperature. The product was extracted into ether (twice), and thecombined etheral extracts were washed with water and dried (MgSO₄). Thesolvent was removed in vacuo to afford a soft off-white solid. Yield19.3 g (95%). The identity of the product was confirmed as above.

Route B2

Step B21 ##STR37##

A solution of 1-bromohexane (60.0 g, 0.36 mol.) in acetone (150 ml) wasadded dropwise to a stirred mixture of 4-bromophenol (71.0 g, 0.41 mol)and potassium carbonate (120.0 g, 0.87 mol) in acetone (600 ml) at roomtemperature. The stirred mixture was heated under reflux (90°-95° C.)for 43 h (ie until glc analysis revealed an absence of 1-bromohexane).The product was extracted into ether (twice), and the combined etherealextracts were wasted with water, 5% sodium hydroxide, water and dried(MgSO₄). The solvent was removed in vacuo and the residue was distilledto yield a colourless liquid. Yield 79.4 g (86%), bp 100°-110° C. at 0.1mm Hg. The identity of the product was confirmed as above.

Step B22 ##STR38##

A solution of the Grignard reagent, prepared from the product of stepB21 (72.0 g, 0.28 mol) and magnesium (7.75 g, 0.32 mol) in dry THF (220ml) was added dropwise to a stirred, cooled (-78° C.) solution oftri-isopropyl borate (109.1 g, 0.58 mol) in dry THF (40 ml) under drynitrogen. The stirred mixture was allowed to warm to room temperatureovernight and stirred for 1 h with 10% hydrocholoric acid (320 ml) atroom temperature. The product was extracted into ether (twice), and thecombined ethereal extracts were washed with water and dried (MgSO₄). Thesolvent was removed in vacuo to afford a colourless solid. Yield 61.2 g(99%) mp 80°-85° C. The identity of the product was confirmed as above.

Route A1

Step A11 ##STR39##

Bromine (44.0 g, 0.275 mol) was added dropwise to a mixture ofbenzonitrile (10.0 g, 0.097 mol) and aluminum chloride (42.0 g, 0.31mol) at room temperature. The mixture was heated at 70° C. for 3.5 h andpoured into ice/water. The product was extracted into ether (twice) andthe combined ethereal extracts were washed with sodium thiosulphate anddried (MgSO₄). The solvent was removed in vacuo to afford an off-whitesolid (23.4 g) (glc analysis revealed presence of three components)which was recrystallised from benzene to give colourless crystals. Yield3.1 g (12%). mp 144°-45° C. (lit 144°-145° C.). The identity of theproduct was confirmed as above.

Note: The low yield was probably due to insufficient reaction time ortoo low a temperature being used as glc analysis of the crude productrevealed the presence of starting material and what is suspected to be3-bromobenzonitrile.

Step A12 ##STR40##

A solution of 4-pentylphenylboronic acid (BID) (2.88 g, 0.015 mol) inethanol (50 ml) was added dropwise to a stirred mixture of2,5-dibromobenzonitrile (1.40 g, 5.36 mol) andtetrakis-(triphenylphosphine) palladium (0) (0.3749 g, 0.325 mmol) inbenzene (30 mi) and 2M-sodium carbonate (30 ml) at room temperatureunder dry nitrogen. The stirred mixture was heated under reflux (90°-95°C.) for 18 h (ie until glc analysis revealed absence of startingmaterial), cooled and stirred for 1 hr at room temperature with 30%hydrogen peroxide (5 ml). The mixture was filtered, the filtrate waswashed with ether (twice), and the combined ethereal phases were washedwith water and dried (MgSO₄). The solvent was removed in vacuo and theresidue was purified by column chromatography [silica gel/petroleumfraction (bp 40°-60° C) - dichloromethane, 2:1] to give a colourlesssolid which was recrystallised from ethanol to yield fine colourlesscrystals. Yield 1.13 g (53%). The identity of the product was confirmedas above. The product showed the following liquid crystal transitions(°C.): K-I 40.0, S_(A) -N (33.5), N-I (38.0)

Step A12 ##STR41##

A solution of 4-hexoxyphenylboronic acid (B22) (3.33 g, 0.015 mol) inethanol (70 ml) was added dropwise to a stirred mixture of2,5-dibromobenzonitrile (1.30 g, 4.98 mmol) andtetrakis-(triphenylphosphine) palladium (0) (0.3554 g, 0.308 mmol) inbenzene (30 ml) and 2M-sodium carbonate (30 ml) at room temperatureunder dry nitrogen. The stirred mixture was heated under reflux (90°-5°C.) for 21 h until glc analysis revealed absence of starting material),cooled and stirred for 1 hr at room temperature with 30% hydrogenperoxide (5 ml). The mixture was filtered, the filtrate was washed withether (twice), and the combined ethereal phases were washed with waterand dried (MgSO₄). The solvent was removed in vacuo and the residue waspurified by column chromatography [silica gel/petroleum fraction (bp40°-60° C.)-dichloromethane, 2:1] to give a colourless solid which wasrecrystallised from ethanol t6 give colourless crystals. Yield 0.87 g(38%).

Route A²

The 4-alkyl-and 4-alkoxy-phenylboronic acids prepared using route Bexemplified above were used to prepare compounds of formula 1.1 viaroute A 2.

Step A21 ##STR42##

N-Bromosuccinimide (NBS) (37.71 g, 0.21 mol) was added in small portionsover 40 mins to a stirred, cooled (-10°-0° C.) solution of2-aminobenzonitrile (25.00 g, 0.21 mol) in dry dichloromethane (150 ml)under dry nitrogen. The mixture was stirred at 0° C. for 1 h 10 mins(glc analysis revealed a complete reaction) and washed with a largeamount of water. The aqueous layer was washed with dichloromethane andthe combined organic phases were washed with water and dried (MgSO₄).The solvent was removed in vacuo to give a red/purple solid (39 g, 94%)mp=92°-94° C.

Step A22 ##STR43##

A stirred mixture of 2-amino-5-bromobenzonitrile (25.00 g 0.13 mmol) and36% (conc) HCl (110 ml) was gently warmed to obtain a solution, thencooled to -5° C. and a solution of sodium nitrite (10.50 g, 0.15 mol) inwater (50 ml) was added dropwise whilst maintaining the temperature at-5° C. The mixture was stirred at 0° C. for 1/2hr. cyclohexane wasadded, a solution of potassium iodide (43.5 g, 0.26 mol) was addeddropwise at between 5 and 10° C. The mixture was stirred at roomtemperature for a few hours (or overnight for convenience), then warmedgently for 10 mins to ensure complete reaction. The product wasextracted into ether (twice), the combined ethereal phases were washedsuccessively with sodium metabisulphite, 10% sodium hydroxide, water anddried (Mg SO₄). The solvent was removed in vacuo to give a sand-colouredsolid (35 g, 87%). mp =113° -114° C

Step A23 ##STR44##

A solution of 4-hexoxyphenylboronic acid (see step B22) (1.56 g, 7.03mmol) in ethanol (minimum amount possible 20 ml) was added dropwise to astirred mixture of 5-bromo-2-iodobenzonitrile (1.80 g, 5.84 mmol) andtetrakis (triphenylphosphine) palladium (0) (abbreviated hereinafter toTTP) (0.35 72 g, 0.31 mmol) in benzene (30 ml) and 2M-sodium carbonate(30 ml). The stirred mixture was heated under reflux (95° C.) for 11/4hr (ie until glc analysis revealed a satisfactory startingmaterial--product ratio (1:10)). The product was extracted into ether(twice), the combined ethereal extracts were washed with brine and dried(MgSO₄). The solvent was removed in vacuo and the residue was purifiedby column chromatography (silica gel/petroleum fraction (bp 40°-60°C.)--dichloromethane, 1:1) to give a colourless solid (1.72 g, 82%).

    ______________________________________                                         ##STR45##                     (2)                                            5-bromo-2-iodobenzonitrile                                                                          2.50 g, 8.12 mmol                                       4-octoxyphenylboronic acid (via route B2)                                                           2.44 g, 9.76 mmol                                       TTP                   0.4927 g 0.43 mmol                                      ______________________________________                                    

The method was the same as that above. The mixture was reheated underreflux (95° C.) for 2 h. Purified by column chromatography [silicagel/petroleum fraction (bp 48°-60° C.)-dichloromethane, 1:1] to give acolourless solid (2.50 g, 80%).

    ______________________________________                                         ##STR46##                     (3)                                            5-bromo-2-iodobenzonitrile                                                                         3.50 g, 0.001 mol                                        4-pentylphenylboronic acid (route B1)                                                              2.53 g, 0.013 mol                                        TTP                  0.6421 g, 0.56 mmol                                      ______________________________________                                    

The method was the same as that above. The mixture was heated underreflux (295° C.) for 2 h. Purified by column chromatography (silicagel/petroleum fraction (bp 40°-60° C.), dichloromethane, 1:1) anddistillation (Kugel rohr, 0.1 mm Hg) to give a give yellow liquid (2.67g, %).

Step A24

    ______________________________________                                         ##STR47##                     (1)                                            4-bromo-2-cyano-4.sup.1 -pentylbiphenyl (A23(3))                                                     0.34 g, 1.0 mmol                                       4-hexoxyphenylboronic acid (B22)                                                                     0.44 g, 1.98 mmol                                      TTP                    0.1645 g, 0.14 mmol                                    ______________________________________                                    

    ______________________________________                                         ##STR48##                     (2)                                            4-bromo-2-cyano-4.sup.1 -hexoxybiphenyl                                                             1.50 g, 4.19 mmol                                       (A23(1))                                                                      4-pentylphenylboronic acid (B13)                                                                    1.05 g, 5.47 mmol                                       TTP                   0.314 g, 0.27 mmol                                      ______________________________________                                    

    ______________________________________                                         ##STR49##                     (3)                                            4-bromo-2-cyano-4.sup.1 -pentylbiphenyl (A23(3))                                                     1.30 g, 3.96 mmol                                      4-octoxypenylboronic acid (via route B22)                                                            1.19 g, 4.76 mmol                                      TTP                    0.265 g, 0.23 mmol                                     ______________________________________                                    

    ______________________________________                                         ##STR50##                     (4)                                            4-bromo-2-cyano-4.sup.1 -octoxybiphenyl                                                             1.48 g, 3.83 mmol                                       (from A23(2)                                                                  4-pentylphenylboronic acid (from B13)                                                               1.01 g, 5.26 mmol                                       TTP                   0.2812 g, 0.34 mmol                                     ______________________________________                                    

In each case the method used was treat of step A23 above. The mixture incase (2) was heated under reflux for 17 hours, in cases (1) and (3) for21 hours, and case (4) for 22 hours, i.e. until analysis revealed acomplete reaction. The product is purified by column chromatography(silica gel/petroleum formation (bp 40-60)-dichloromethane 1:1) toafford solids which were recrystallised from ethanol. The product of (2)was pale yellow and so was decolourised with charcoal.

Yield:

(1) colourless crystals (0.26%, 61%)

(2) colourless plates (0.80 g, 44%)

(3) colourless crystals (1.18 g, 66%)

(4) colourless solid (1.16 g, 67%)

EXAMPLE 2

Using route C1 the following compounds of structure 1.3 were prepared:

    ______________________________________                                         ##STR51##                                                                    R.sub.1 R.sub.2    Liquid Crystal Transition Temp                             ______________________________________                                        n-C.sub.5 H.sub.11                                                                    OC.sub.8 H.sub.17 -n                                                                     K 62.0 SA 160 I                                            n-C.sub.5 H.sub.11                                                                    OC.sub.6 H.sub.13 -n                                                                     K 62.0 SA 163.5 I                                          ______________________________________                                    

Step C11

    ______________________________________                                         ##STR52##                                                                    2-hydroxybenzonitrile                                                                             A 7.50 g, 0.063 mol                                                           B 8.10 g, 0.068 mol                                       1-bromo-octane      A 14.00 g, 0.127 mol                                      1-bromohexane       B 13.50 g, 0.082 mol                                      Potassium Carbonate A 17.50 g 0.127 mol                                                           B 18.77 g 0.136 mol                                       ______________________________________                                    

The experimental procedure was the same as for Step B21 described above.Yield: A 13.909 (96%) bp 130°-135° at 0.05 mm Hg; B 13.11 g (95%) bp115°-518° at 0.1 mm Hg.

Step C12

    ______________________________________                                         ##STR53##                                                                    Bromine           A 18.70 g, 0.117 mol                                                          B 19.32 g 0.12 mol                                          C11 product       A 13.50 g, 0.058 mol                                                          B 12.25 g, 0.060 mol                                        ______________________________________                                    

The bromide was added dropwise during 15 minutes to a stirred solutionof the C11 product in chloroform (30 ml) at room temperature. Thestirred solution was refluxed for 42 hours (glc showed a completereaction). The cooled solution was washed with sodium metabisulphite,water, then dried (Mg SO₄). The solvent was removed vacuo in give anoff-white solid. Yield: A 17.50 g (97%) mp 36°-37°, B 16.10 g (95%) lowmelting around 15°.

Step C13

    ______________________________________                                         ##STR54##                                                                    4'-bromo-4-pentylbiphenyl                                                                              9.35 g                                               magnesium               0.871 g                                               tri-isopropyl borate    11.66 g                                               ______________________________________                                    

The experimental procedure was the same as for steps B13 and B22. Thecrude yield was 8.29 g, 100%.

Step C14

    ______________________________________                                         ##STR55##                                                                    (A)       C12 product (A) 1.55 g, 5.00 mmol                                             C13 product     1.75 g, 6.53 mmol                                             TPP             0.38 g, 0.33 mmol                                   (B)       C12 product (B) 1.55 g, 5.50 mmol                                             C13 product     1.91 g, 7.13 mmol                                             TTP             0.39 g, 0.34 mmol                                   ______________________________________                                    

The experimental procedure was the same as for Step A23 above. The crudeproduct was purified by column chromatography (silica gel/petroleumfraction (bp 40°-60°) dichloromethane 2:1) to give a colourless solidwhich was recrystallised from ethanol-ethylacetate (2:1) to yieldcolourless crystals. Yield: A 1.85 g (82%), B 1.10 g (47%).

EXAMPLE 3

Using route E1 the compound of structure 1.10: ##STR56## was prepared.Liquid crystal transitions were K 48.0 S_(A) 118.0 I.

Step E11

    ______________________________________                                         ##STR57##                                                                    4'-bromo-2-fluro-4-pentylbiphenyl                                                                      9.90 g                                               Magnesium               0.871 g                                               Triisopropylborate      11.66 g                                               ______________________________________                                    

The experimental procedure was the same as for Step B13 above. Crudeyield: 8.85 g, 100%.

Step E12

    ______________________________________                                        5-bromo-2-octoxybenzonitrile (C12A)                                                                  1.30 g, 4-19 mmol                                      E11 product            1.56 g, 5.45 mmol                                      TTP                    0.28 g, 0.24 mol                                       ______________________________________                                    

The experimental procedure was the same as for step A23 above. The crudeproduct was purified by column chromatography (silica gel/petroleumfraction (bp 40°-60°) dichloromethane 2:1) to give a colourless solidwhich was recrystallised from ethanol to give colourless crystals.

EXAMPLE 4

Using route D2 the following compounds of structure 1.4 was prepared:

    ______________________________________                                         ##STR58##                                                                    R.sub.1   R.sub.2  Liquid Crystal Transition Temps                            ______________________________________                                        n-C.sub.6 H.sub.13 O                                                                    nC.sub.5 H.sub.11                                                                      K 100.5 S.sub.A 167.0 I                                    n-C.sub.8 H.sub.17 O                                                                    nC.sub.5 H.sub.11                                                                      K 100.0 S.sub.A 163.5 I*                                   ______________________________________                                         *The extrapolated dielectric anistropy ΔE of the compound was           measured to be -9.5.                                                     

Step D21

    ______________________________________                                         ##STR59##                                                                    (A)        4-bromo-3-fluorophenol                                                                            6.00 g                                                    1-bromo-octane      7.30 g                                                    potassium carbonate                                                                              10.00 g                                         (B)        4-bromo-3-fluorophenol                                                                           10.00 g                                                    1-bromohexane      10.37 g                                                    potassium carbonate                                                                              14.50 g                                         ______________________________________                                    

The experimental procedure was the same as for Step B21 above. Yields: A9.01 g, 96% as a colourless liquid bp 140°-142° at 0.5 mm Hg; B 13.71 g,96%.

Step D22

    ______________________________________                                         ##STR60##                                                                    (A)       Step D21 product                                                                              2.00 g, 6.60 mmol                                             Step C13 product                                                                              2.30 g, 8.58 mmol                                             TTP             0.60 g, 0.52 mmol                                   (B)       Step D21 product                                                                              1.50 g, 5.45 mmol                                             Step C13 product                                                                              1.90 g, 7.10 mmol                                             TTP             0.50 g 0.43 mmol                                    ______________________________________                                    

The experimental procedure was the same as for Step A23 above. The crudeproducts were purified by column chromatography (silica gel/petroleumfraction (bp 40°-60° ) dichloromethane, 3:1) to yield colourless solidswhich were recrystallised from ethanol-ethyl acetate (2:1) to yieldcolourless crystals. Yield: A 2.30 g, 78%; B 1.46 g, 64%.

These products showed liquid crystal phases as below:

(A) K 69.0 (S_(K) 25.0 S_(J) 43.0) S_(C) 119.0 N 158.0 I

(B) K 83.5 (S_(K) 48.5 S_(J) 62.0) S_(C) 105.0 N 166.0 I

Step D23

    ______________________________________                                         ##STR61##                                                                    (A)   Step D22 product                                                                           1.50 g, 3.36 mmol                                                n-butyl lithium                                                                            0.50 ml 10.0M in hexane, 5.00 mmol                         (B)   Step D22 product                                                                           1.25 g, 2/99 mmol                                                n-butyl lithium                                                                            1.20 ml 2.5M in hexane, 3.00 mmol                          ______________________________________                                    

The solution of n-butyl lithium was added dropwise to the solution ofthe appropriate D22 product in dry THF (80 ml) under dry nitrogen withstirring, cooled to -78° C. In the case of (A) the mixture wasmaintained under these conditions for 6 hours, and for (B) for 5 hours.The mixture was then poured into a solid CO₂ /ether slurry. 10%hydrochloric acid was added, the aqueous layer was washed with ether andthe combined ethereal extracts were washed with water and dried (MgSO₄). The solvent was removed in vacuo to give colourless solids.Yields: (A) 1.65 g, (B) 1.45 g (tic analysis revealed the presence ofsome starting materials).

Step D24

    ______________________________________                                         ##STR62##                                                                    (A)       Step D23 product                                                                              1.65 g 3.37 mmol                                              oxalyl chloride 1.00 g 7.87 mmol                                              35% ammonia     30 ml                                                         DMF             8 drops                                                       thionyl chloride                                                                              4.10 g, 0.034 mol                                   (B)       Step D23 product                                                                              1.45 g 3.14 mmol                                              oxalyl chloride 0.80 g 6.30 mmol                                              35% ammonia     25 ml                                                         DMF             2 drops                                                       thionyl chloride                                                                              3.70 g, 0.03 mol                                    ______________________________________                                    

A solution of the oxalyl chloride in dry benzene (30 ml) was addeddropwise to a stirred solution of the Step D23 product and DMF in drybenzene (30 ml) at room temperature. The mixture was stirred at roomtemperature overnight and the excess of oxalyl chloride and benzene wereremoved in vacuo. The residue was dissolved in diglyme (10 ml) and addeddropwise to the gently stirred 35% ammonia. the resulting precipitatewas filtered off and dried (Ca Cl₂) in vacuo (0.1 mm Hg) to give acolourless solid. A solution of the thionyl chloride in dry DMF (30 ml)was added dropwise to a stirred solution of this solid in dry DMF (30ml). The mixture was stirred at room temperature overnight and pouredonto ice/water. The product was extracted into ether (twice), thecombined ethereal extracts were washed with water, sodium hydrogencarbonate, water and dried (MgSO₄). The solvent was removed in vacuo andthe residue was purified by column chromatography [silica gel/petroleumfraction (bp 40°-60° C.)-dichloromethane, 2:1] to give a colourlesssolid. Inthe case of (A) this was recrystallised from ethyl acetate, and(B) from ethanol-ethyl acetate (2:1) to yield colourless crystals. YieldA: 0.21 g, 13% based on D22 product; B 0.20 g, 15% based on D22 product.

EXAMPLES OF LIQUID CRYSTAL MIXTURES EXAMPLE 5

Properties of mixtures of two cyano-terphenyls of formula 1.1, ie (A)where both R and R are n-pentyl, and (B) where both R¹ and R² aren-hexyloxy, with an FTP of formula: ##STR63## are listed below togetherwith properties of the pure FTP.

EXAMPLE 5

    __________________________________________________________________________             Transitions (°C.)                                                      K      S.sub.B                                                                              S.sub.C                                                                              S.sub.A                                                                              N      I                                 __________________________________________________________________________    100% FTP .  46  .  (35)                                                                              .  52.2                                                                              .  89  .  126.5                                                                             .                                   95% FTP                                                                              .  42.5                                                                              .  --  .  48  .  80  .  122 .                                  5% (A)                                                                         85% FTP                                                                              .  36  .  --  .  39  .  60.5                                                                              .  113 .                                  15% (A)                                                                        94% FTP                                                                              .  44  .  --  .  55.5                                                                              .  82  .  125 .                                  6% (B)                                                                         85% FTP                                                                              .  44  .  --  .  56  .  78  .  123 .                                  15% (B)                                                                      __________________________________________________________________________

From these results it is clear that the mixing of a cyanoterphenyi ofthe invention with an FTP suppresses the S_(B) phase of the FTP, in somecases lowers the temperature at which the S_(C) phase of the FTP appearson heating, and in others broadens the temperature range over which theS_(C) phase persists.

In the following examples the following mixtures and compounds arereferred to by the abbreviations indicated:

Mixture H1 ##STR64## (ie a mixture of FTP's of formula IIA (Y=F)described above) This mixtures shows liquid crystal transitiontemperatures: K 31.8 S_(?) 40.4 S_(??) 50.6 S_(C) 107 N 160 I

Mixture H2 ##STR65##

(ie a mixture of FIT's of formula lIB and IIC described above) Thismixture shows liquid crystal transition temperatures: <20 Sc 96.9 N146.2 I

Mixture H3 ##STR66##

(ie a mixture of compounds of formula IlIA)

This mixture shows liquid crystal transition temperatures: S_(?) 41.5 Sc87 S_(A) 120.7 N 134.5 I ##STR67##

(ie formula VII described above)

EXAMPLE 6 ##STR68## Addition of the cyanoterphenyl results in increasedSc range and elimination of low temperature undesirable smectic phasesrelative to pure H1. EXAMPLE 7 ##STR69## Increased Sc range, eliminationof lower smectic phases. EXAMPLE 8 ##STR70## Supercooled to much lowertemperature than pure }t3, no lower smectic phases. EXAMPLE 9

    ______________________________________                                        Mixture H2              72      wt %                                           ##STR71##              18      wt %                                          Dopant 1                6.25    wt %                                          Dopant 2                3.75    wt %                                          <20 Sc 90 S.sub.A 124 N 133 I                                                 ______________________________________                                    

This mixture shows a room temperature Sc phase, with a highertemperature S_(A) phase which assists alignment in a liquid crystaldevice. Switching response time (μsec) at various peak voltages withzero volts AC bias at 30° C., and spontaneous polarisation Ps at varioustemperatures using a 2 μm polyimide aligned cell are tabulated below:

    ______________________________________                                        Peak voltage            Temp    P                                             (v)        Resp. time   (°C.)                                                                          (nC/cm.sup.2)                                 ______________________________________                                        10         205          80      2.0                                           15         99           70      4.5                                           20         63           60      6.7                                           25         46           50      8.1                                           30         38           40      9.3                                           35         31           40      9.3                                           40         27           30      10.5                                          45         23                                                                 50         21                                                                 55         19                                                                 60         17                                                                 65         16                                                                 ______________________________________                                    

As 30° C. the cone angle was found to be 23°.

EXAMPLE 10

    ______________________________________                                        Mixture H2              72     wt %                                            ##STR72##              18     wt %                                           Dopant 1                5.8    wt %                                           Dopant 2                4.2    wt %                                           20 Sc 91.5 SA 123.7 N 133.7 I                                                 ______________________________________                                    

Switching response times (μsec) at various AC bias voltages, at 30° C.using a 1.9 μm polyimide aligned cell are tabulated below. The coneangle was 23°.

    ______________________________________                                        Peak Voltage                                                                             Resp time   Resp time Resp time                                    (v)        0V AC       5V AC     10V AC                                       ______________________________________                                        10         1300        995       530                                          15         287         283       280                                          20         155         174       219                                          25         127         130       192                                          30          88         114       213                                          35          77         125                                                    40          81         233                                                    45         124         366                                                    50         300         467                                                    ______________________________________                                    

Using a 6 μm polyimide aligned cell the Ps at various temperatures wasmeasured and tabulated below.

    ______________________________________                                        Temp (°C.)                                                                           Ps (nC/cm.sup.2)                                                ______________________________________                                        80            1.3                                                             70            2.5                                                             60            3.4                                                             50            4.0                                                             40            4.4                                                             30            4.9                                                             ______________________________________                                    

EXAMPLE 11 (COMPARATIVE)

To illustrate the advantages of use of the terphenyls of the inventionin liquid crystal materials two mixtures were prepared containingmixture H2 without a terphenyl of the invention, and proportions ofdopants 1 and 2 the same as or very close to those used in the mixturesof examples 9 and 10, identified as mixtures 9A and 10A below.

    ______________________________________                                                      9A        10A                                                   ______________________________________                                        Mixture H2      90 wt %   90 wt %                                             Dopant 1      6.25 wt % 5.63 wt %                                             Dopant 2      3.75 wt % 4.37 wt %                                             ______________________________________                                         Their properties were:                                                        9A: 20 Sc* 90.4 SA 109.6 N 133 I                                              10A: 20 Sc* 93 SA 109.6 N 133 I                                          

Hence these two mixtures retain useful Sc phase up to virtually the sametemperature as the mixtures of Examples 9 and 10 respectively.

At 30° C. mixtures 9A and 10A showed the following Ps and minimumswitching response times (T min) (μ1 sec) at the voltage (Vmin) and ACbias shown, the corresponding values for mixtures 9 and 10 being givenfor comparison.

    ______________________________________                                        Mix-  0V AC       5V AC       10V AC                                          ture  T min   V min   T min V min T min V min Ps                              ______________________________________                                        9     (17 μsec at 60 V, no V min observed)                                                                   10.5                                        9A    23      50       36   40    --    --    8.96                            10    77      35      114   30    192   25    4.9                             10A   86      35      149   30    243   20    4.24                            ______________________________________                                    

From this stable it can be seen that mixtures 9 and 10, which contain aterphenyl of the invention, have a higher Ps and faster switching timesthan the corresponding mixtures 9A and 10A which lack such a terphenyl.

An example of the use of a compound of Formula I in a liquid crystalmaterial and device embodying the present invention will now bedescribed with reference to the accompanying drawing, FIG. 12 which is across sectional end view of a liquid crystal shutter.

In FIG. 12a liquid crystal cell comprises a layer 1 of liquid crystalmaterial exhibiting a nematic or chiral smectic C phase, between a glassslide 2 having a transparent conducting layer 3 on its surface, eg oftin oxide or indium oxide, and a glass slide 4 having a transparentconducting layer 5 on its surface. The slides 2,4 bearing the layers 3,5are respectively coated by films 6,7 of a polyimide polymer. Prior toconstruction of the cell the films 6 and 7 are rubbed with a soft tissuein a given direction the, rubbing directions being arranged parallelupon construction of the cell. A spacer 8 eg of polymethylmethacrylate,separates the crystal material 1 is introduced between the slides 2,4 byfilling the space between the slides 2, 4 and spacer 8 and sealing thespacer 8 in a vacuum in a known way,

Suitable materials for the layer 1 of liquid crystal are the mixtures ofexamples 9 and 10 above, with a spacing between the films 6 and 7 ofabout 2 μm.

We claim:
 1. A ferroelectric smectic liquid crystal material being amixture of compounds wherein at least one of the said compounds is alaterally cyano-substituted terphenyl having the Formula I: ##STR73##wherein R¹ and R² are independently selected from hydrogen or C₁₋₁₅alkyl, alkoxy, or alkyl or alkoxy in which one or more CH₂ groups arereplaced by O, COO, OOC, CHX, CX₂, CH=CX, CX=CH, CX=CX, where X isfluorine or chlorine, CRCN where R is alkyl, or C.tbd.C, or in which aterminal CH₃ of the alkyl or alkoxy chain is replaced by CF₃, n is 0 or1, and the F substituents, if present, and the CN substituent areindependently located in any of the available substitution positions. 2.The ferroelectric smectic liquid material according to claim 1 whereinone of the compounds of Formula I has the Formula IA: ##STR74## whereinR¹ and R² are independently alkyl, alkoxy or alkynyl, and the terphenylhas a subsitution pattern selected from one of the followingsubstitution patterns: (D=CN), (A=CN), (B=F, G=CN), (A=CN, S=F), (n=CN),(C=CN, D=F), (A=F, G=CN), (A=F, E=CN), (B=F, E=CN), (B=F, D=CN), (A=F,D=CN), (A=F, C=CN), (S=F, C=CN), (A=F, S=CN) the remainder lateralsubstitution positions being occupied by hydrogen.
 3. The ferroelectricsmectic liquid crystal material according to claim 2 wherein R¹ and R²are independently selected from n-alkyl or n-alkoxy containing 3-12carbon atoms.
 4. The ferroelectric smectic liquid crystal materialaccording to claim 3 wherein one of the compounds of Formula IA has theformula: ##STR75##
 5. The ferroelectric smectic liquid crystal materialaccording to claim 3 wherein one of the compounds of formula IA has theformula: ##STR76##
 6. The ferroelectric smectic liquid crystal materialaccording to claim 3 wherein one of the compounds of formula has theformula: ##STR77##
 7. The ferroelectric smectic liquid crystal materialaccording to claim 3 wherein one of the compounds of formula has theformula: ##STR78##
 8. The ferroelectric smectic liquid crystal materialaccording to claim 3 wherein one of the compounds of formula IA has theformula: ##STR79##
 9. The ferroelectric smectic liquid crystal materialaccording to claim 1 wherein said ferroelectric smectic liquid crystalmaterial additionally contains one or more fluorinated terphenyls of theformula: ##STR80## where R³ and R⁴ are independently selected fromhydrogen, alkyl and alkoxy each containing 1-12 carbon atoms, p may be 1or 2, and the fluoro substituent or substituents may occupy any of theavailable lateral substitution positions.
 10. The ferroelectric smecticliquid crystal material according to claim 9 wherein the fluorinatedterphenyl has a formula selected from one of the following: ##STR81##11. The ferroelectric smectic liquid crystal material according to claim1 where said ferroelectric smectic liquid crystal material additionallycontains at least one compound of the formula: ##STR82## wherein R^(A)and R^(C) independently contain 1-12 carbon atoms, R^(A) is n-alkyl orn-alkoxy, R^(C) is n-alkyl.
 12. The ferroelectric smectic liquid crystalmaterial according to claim 1 where said ferroelectric smectic liquidcrystal material additionally contains at least one optically activecompound of the formula: ##STR83## wherein R^(A) is C₅ -C₁₂ n-alkyl orn-alkoxy, (F) indicates that the adjacent phenyl ring may carry a fluorosubstituent, and R^(B) is C₁ -C₄ n-alkyl, C₃ C₆ cycloalkyl, or abranched alkyl group of the formula: ##STR84## where a is 0 or aninteger 1-6 and each of b and c is an integer 1-6.
 13. A liquid crystaloptical display device comprising two substantially parallel substratesat least one of which is optically transparent and having electrodes ontheir facing surfaces, and a ferroelectric smectic liquid crystalmaterial according to claim 1.